In general, semiconductor memory devices are roughly classified into volatile memory devices and non-volatile memory devices. Most of the volatile memory devices are random access memory (RAM) such as dynamic random access memory (DRAM), static random access memory (SRAM), etc. Volatile memory devices are devices that, when power is supplied to the volatile memory, it is possible to input and preserve data, but, when power to the volatile memory is interrupted, the information therein is lost.
Conversely, most of the non-volatile memory devices are read only memory (ROM), and thus it is possible to preserve data even when power to the device is interrupted.
Currently, on the process technology side, the non-volatile memory device is classified into a floating gate group and a metal/insulator/semiconductor (MIS) group in which dielectric films of two or more types are layered to be two or three floor.
The non-volatile memory device of the floating gate group stores data using potential well, and currently, the representative structure thereof is an EPROM tunnel oxide (ETOX) structure that is widely applied to an electrically erasable programmable read only memory (EEPROM).
On the other hand, the non-volatile memory device of the MIS group memorizes data using traps that exist in dielectric film bulk, an interface between dielectric films, and an interface between a dielectric film and a semiconductor. Currently, the representative structure thereof is a metal/silicon ONO semiconductor (MONOS/SONOS) structure that has been used as an EEPROM.
Conventional arts relating to a flash memory having the SONOS structure are disclosed in U.S. Pat. Nos. 6,440,797; 6,444,545; 5,424,569; and 5,387,534.
FIG. 1 is a cut view showing a non-volatile memory device having a conventional SONOS structure, and, as shown in FIG. 1, phosphorus is injected into a semiconductor substrate 1 to form a first semiconductor region 2, and an ONO layer 3 having a oxide/nitride/oxide laminated structure is formed thereon, and then polysilicon layer 4 is formed on the ONO layer 3, such that the SONOS structure of a semiconductor/ONO/semiconductor structure is accomplished.
In a method of fabricating a non-volatile memory device having such conventional SONOS structure, because a photo-engraving process has to be carried out repeatedly, there is a problem of complicated process, much manufacturing time, and much cost to manufacture.